1. Technical Field
This disclosure relates to aircraft windows and windshields, and, in particular, to a system for draining, dissipating or discharging static charge, such as precipitation static (p-static) charge, from an aircraft window or windshield, while not providing a significant ground path for lightning strikes.
2. Discussion of Related Art
Windows and windshields used in aircraft typically include multiple glass and/or plastic layers or plies which are fused or laminated together to form a composite transparent window. It is noted that throughout this disclosure, the terms “window” and “windshield” are interchangeable and will be used as if they are interchangeable, unless indicated otherwise, either explicitly or implicitly by the context. During aircraft flight, fog, mist, water, ice, etc., can be deposited on the outside surface of the window. In order to remove these, aircraft windshields typically include an internal electrical device for heating the windshield. In addition to fog, water, mist, ice, etc., static electric charge also collects on the outside surface of an aircraft window during flight. If allowed to build up, the static charge reaches an electric potential sufficient to discharge through the window to the interior heating device.
This electrical discharge often punctures small holes in the outer ply of the window. In extreme cases, depending on the dielectric strength of the window material, a relatively high voltage discharge can result in sufficient localized heat to severely damage the window in the vicinity of the discharge path. Furthermore, when the discharge is through the outer ply and into the heating device, the heating device and other associated electrical components can be severely damaged. It is therefore desirable to provide some facility for dissipating static charge before it reaches an electric potential sufficient to discharge through the window.
Highly conductive or low-resistance wires can be used to connect the outside surface of the window to aircraft ground to dissipate or discharge the static ground. Unfortunately, such wires also present a ground to lightning. That is, as a result of lightning strikes seeking low-resistance paths to ground, these conductive paths can ground extremely high currents into the window and the window heater electrical system, which can cause permanent damage to the window and the window controller or any protective shunts in the system.